JP5036726B2 - Method for etching a substrate for photolithography - Google Patents

Description

(Cross-reference to related applications)
This application claims priority from US Provisional Application No. 60 / 751,349 (Title of Invention: Improved Etching Method for Photolithographic Substrates) filed by the applicant on December 16, 2005. This application is related to the provisional application, the contents of which are cited within this specification.
(Field of Invention)
The present invention relates generally to semiconductor processing, and more particularly to an improved method of etching a photolithography substrate.

(background)
In order to improve device performance, its circuit density continues to rise. Such an increase in circuit density is realized by a reduction in the size of the feature. The target feature size of the current technology is 0.15 microns, which is expected to decrease to 0.13 microns in the near future.

  The exact value of the feature dimension in the device depends on every step in the processing process. The vertical method dimensions are determined by the doping and layer formation processes, while the horizontal dimensions are mainly determined by the photolithography process. The width and space of the wiring forming the circuit pattern are often referred to as critical dimensions (CD).

  Photolithography is a technique used to form an accurate circuit pattern on a substrate surface. These patterns are then transferred to the wafer structure by an etching or vapor deposition process. Ideally, a pattern that completely matches the design dimension (accurate dimension) is formed at the design position by a photolithography process (referred to as alignment or registration).

  Photolithography is a process including a plurality of steps, in which a desired pattern is first formed on a photomask (or reticle). The pattern is transferred to the substrate by a photomasking process. In this step, for example, a UV-sensitive coating layer on the substrate is exposed to the same line through a patterned photomask. The coating layer (photoresist) changes chemically when exposed to the same line, providing a more or less soluble photosensitive area for subsequent development. Photolithographic techniques are well known in the relevant industry. These techniques are described in the text “Introduction to Microlithography” edited by Thompson et al.

  Since the photomask is the original circuit pattern formed on a large number of substrates, any imperfections introduced in the process of manufacturing it are reproduced on all wafers imaged with the photomask. It will be. Therefore, the production of a high-quality photomask that faithfully reproduces the design pattern and dimensions is extremely important for realizing a high yield device manufacturing process.

Two major photomask reticles are well known in the relevant industry: absorption and phase shift. An absorptive photomask is typically composed of an optically transparent substrate (eg, fused silica, CaF _2, etc.) coated with an opaque film (eg, Cr). The opaque film may be composed of a single layer or a plurality of substances (for example, an antireflection film (AR chrome) formed on a lower chromium layer. When a two-layer chromium photomask is used, Examples of commonly used opaque films include, but are not limited to: AR8, NTAR7, NTAR5, TF11 and TF21 (all trade names) In the photomask manufacturing process, the opaque film is transparent. A photoresist layer is then formed on the opaque film and patterned (eg, by sensitizing with a laser beam or an electron beam). The part is developed, and the underlying opaque film to be removed is exposed to the beam, and then the exposed part is removed by an etching process. To form an absorption-type photo mask.

Two types of phase shift masks are well known in the relevant industry: Levenson and halftone. A Levenson type phase shift photomask is typically comprised of an optically transparent substrate (eg, fused silica, CaF _2, etc.) coated with an opaque film (eg, Cr or antireflective Cr). In the photomask manufacturing process, the opaque film is formed on a transparent substrate. A photoresist layer is then formed on the opaque film and patterned with a laser beam or an electron beam. When the photoresist layer is exposed, the portion is developed, and the underlying opaque film to be removed is exposed to the beam. Next, the exposed portion is removed by an etching process, and the underlying substrate is exposed. A second process is used to etch the underlying substrate to the correct depth. As is known in the relevant art, a second photoresist coating and development may optionally be applied to the substrate prior to performing the second etching step.

Half-tone phase shifting photomasks (EAPSM) are typically coated with a film or laminate to attenuate transmitted light while shifting the phase by 180 degrees at the desired wavelength. And an optically transparent substrate (for example, fused quartz, CaF _2, etc.). An opaque film or a laminated film (eg, fused quartz, CaF _2, etc.) is formed on the phase shift material. A photoresist layer is then formed and patterned on the opaque film (using a laser beam or electron beam). When the same photoresist layer is exposed to the same beam, that portion is developed, and the underlying opaque film to be removed is exposed. Next, the opaque film exposed in the etching process is removed, and the underlying phase shift / attenuation film or laminated film is exposed. Following the opaque film etching step, a second etching step is performed to etch the phase shift layer. The process stops at the underlying substrate. As an alternative, an etch stop layer may be formed between the phase shift layer and the substrate. In this case, the second etching step selectively stops at the etching stop layer.

  Ideally, the etch process produces features with smooth vertical sidewalls that accurately reproduce the pattern of the original mask (e.g., photoresist) while the top etch resistant mask (e.g., photoresist, electronic, etc.). High etch selectivity for both the beam resist, etc.) and the underlying material (eg substrate or etch stop layer). Wet etching processes (eg, chloric acid and ceric ammonium nitrate aqueous solutions for antireflective Cr / Cr etching) have high etch selectivity to the etching mask and underlying substrate, but are isotropic As a result, the profile of the etched feature is tilted due to significant undercutting. The CD of the feature after the etching process changes due to the undercut and the inclination of the profile of the feature. Undesirable changes in the CD and / or tilted feature profile impair the optical performance of the final photomask product.

  The dry etching (use of plasma) process is a well-known alternative to wet etching. Plasma etching provides etching results that are more anisotropic than wet etching. Dry etching is a commonly used method for making all three types of masks. In the case of a two-layer chromium photomask, a mixture of a chlorine-containing gas and an oxygen-containing gas is typically used. To improve process performance, additional gas components such as inert gases and deactivators are used.

Early dry etching for photomask fabrication used a low density (˜10 ⁹ ions / cm ³ ) plasma in a capacitively coupled (diode) reactor. At present, dry etching of most photomasks is performed with high-density (10 ¹⁰ to 10 ¹² ions / cm ³ ) plasma (eg, inductively coupled plasma (ICP), transformer coupled plasma (TCP), electron cyclotron resonance (ECR), etc. ) Is used.

In the case of dry etching of a two-layer chromium photomask, the process typically consists of three main steps. In the first step, the antireflection film is removed using a chlorine-containing plasma (for example, Cl ₂ , HCl, CCl ₄ , BCl _3, etc.). In some cases, the anti-reflective chromium etching process is performed using an oxygen-containing gas (eg, O ₂ , CO, CO ₂ , N ₂ O, NO) as well as an inert gas (eg, He, Ar, Ne, Xe, Kr, etc.). ₂ , SO _2, etc.) or an inert gas (eg, He, Ar, Ne, Xe, Kr, etc.) may be used. The first step may be stopped on a timed basis or may be stopped at the reflective Cr / Cr interface using end point technology (eg, laser reflection spectroscopy, optical emission spectroscopy).

  The second step etches most of the Cr material and stops at the underlying film or substrate. The process gas for the second step typically contains a chlorine source and an oxygen source. As with the first step, the process gas mixture may also contain an inert gas. Furthermore, the first and second steps may be performed under the same process conditions. Optionally, the second step may be stopped using endpoint technology.

  The third step is an over-etching step for ensuring complete cleaning of portions with different Cr amounts. This over-etching process is also employed to improve the gradient profile found in parts where the Cr density is low. Increasing the excess etch time completely wipes out the high Cr density portion and improves the feature profile (more pronounced vertical profile), but at the same time promotes more lateral etching and increases CD bias. The overetching process may employ the same operating factors as the first process and / or the second process. The overetching process period is typically determined based on the ratio of the period of the previous process.

  In order to improve the profile of the etching mask (eg, photoresist), a scum removal or trimming step may optionally be performed before the antireflective Cr is etched.

  While the plasma etch process gives higher anisotropy results than the wet etch process, it still causes dimensional changes in the patterned material. The decrease or increase in CD that occurs during the etching process is referred to as “CD bias”. The CD bias for the etching process can be calculated by subtracting the original feature CD before the etch process from the final feature CD after the etch process. It is desirable to minimize the degree of lateral etching that results from increased CD bias.

  If the process CD bias is non-zero, CD bias uniformity must be considered. CD bias uniformity is the distribution of bias values relative to the average CD bias. The CD bias uniformity can include both systematic and random components. One example of systematic non-uniformity seen during photomask etching is non-uniformity corresponding to local etch loading effects (eg, microloading effects or loading effects).

  A phenomenon commonly referred to as “load dependency” is known in the art of dry etching processes. Load dependency means the relationship between the area of exposed material to be etched and its etch rate. For example, in the case of dry etching of a two-layer chromium photomask, the vertical etching rate decreases in a region where the Cr density is high. Assuming that the lateral etching rate is also load-dependent, it is reasonable to think that the higher the Cr density, the lower the CD bias, and the lower the lateral etching rate. However, the opposite phenomenon is actually observed. That is, features with high Cr density (low vertical etch rate) typically have higher CD bias than regions with lower Cr density (lower Cr load).

  In order to evaluate the CD performance of the etching process, two factors need to be considered: the lateral etch rate in the Cr stack and the final profile of the etched features. In the case of Cr etching (the pattern includes areas with different Cr loads), features in areas with higher Cr density (higher photoresist density or higher transparency) are typically etched at a lower rate. Although (as expected), it shows a larger CD bias compared to the lower Cr load region (this is not as expected).

  There is a need for an improved method for the fabrication of photomasks with improved feature profiles and CD performance.

  None of the prior art provides the advantages associated with the present invention.

  Accordingly, it is an object of the present invention to provide an improved method that eliminates the inadequacy contained in prior art devices and makes a substantial contribution to the development of semiconductor processing technology.

  Another object of the present invention is to provide a method for processing a photolithographic substrate, the method comprising the following steps: mounting the photolithographic substrate in a vacuum chamber; A step of cooling to a target temperature, a step of introducing at least one process gas into the vacuum chamber, a step of igniting plasma from the process gas after the cooling step, and a substrate for photolithography using the plasma And a step of removing the photolithographic substrate from the vacuum chamber.

  Yet another object of the present invention is to provide a method for processing a photolithographic substrate, the method comprising the following steps: mounting the photolithographic substrate on a substrate support in a vacuum chamber; A step of controlling the substrate temperature for the photolithography by a fluid, a step of introducing at least one process gas into the vacuum chamber, a step of igniting a plasma from the process gas, and for the photolithography using the plasma A step of processing the substrate, and a step of removing the substrate for photolithography from the vacuum chamber.

  Yet another object of the present invention is to provide a method for etching a photolithography substrate, which includes the following steps: mounting the photolithography substrate on a substrate support in a vacuum chamber. Introducing at least one process gas into the vacuum chamber; igniting a first plasma from the process gas; using the first plasma under a first set of process conditions Etching the photolithography substrate, cooling the photolithography substrate to a target temperature, igniting a second plasma from the process gas after the cooling step, Etching the photolithographic substrate under a second set of process conditions, and using the photolithographic substrate. Step of removing from the vacuum chamber.

  Yet another object of the present invention is to provide a method for controlling the substrate temperature using a large thermal mass during the plasma process, which includes the following steps: adjusting the substrate temperature to the target temperature. A step of mounting the substrate on a substrate support in a vacuum chamber, a step of introducing at least one process gas into the vacuum chamber, a step of igniting plasma from the process gas, and A step of processing the substrate for photolithography, and a step of removing the substrate for photolithography from the vacuum chamber.

  Yet another object of the present invention is to provide a method for etching a photolithography substrate, which includes the following steps: mounting the photolithography substrate on a substrate support in a vacuum chamber. Introducing at least one process gas into the vacuum chamber; igniting a plasma from the process gas; using the plasma at a first target temperature and a first set of process conditions Etching the same photolithographic substrate, etching the same photolithographic substrate under a second target temperature and a second set of process conditions using the plasma, and for the photolithographic process A step of removing the substrate from the vacuum chamber.

  In the above, some actual conditions related to the present invention have been outlined. These facts should be considered merely illustrative of some of the more prominent features and applications of the present invention. Many other advantages may be obtained by implementing or modifying the invention disclosed herein in different ways within the disclosed scope. Accordingly, in addition to the scope of the present invention as defined by the claims, reference should be made to the summary of the invention and detailed description of the preferred embodiments taken in conjunction with the accompanying drawings to provide an understanding of the other aspects of the invention and to make it more understandable. A deep understanding is expected.

(Summary of Invention)
In summary, the present invention relates to an improved method for etching a photolithographic substrate using a plasma system.
A feature of the present invention is that a photolithographic substrate (for example, a two-layer chromium photomask or an embedded attenuated phase shift mask (halftone phase shift photomask)) mounted on a substrate support in a vacuum chamber Is to provide a method of processing. The method includes the step of cooling the photolithographic substrate to a target temperature (eg, a temperature lower than about −30 ° C.). Thereafter, the substrate is subjected to processing such as etching using plasma in a vacuum chamber. The cooling of the photolithographic substrate may be performed in a vacuum chamber in which it is processed, or may be performed in another chamber (the vacuum does not necessarily need to be maintained). At least one process gas (for example, chlorine-containing and oxygen-containing gas) is introduced into the vacuum chamber. The chlorine containing gas may be introduced at a rate greater than about 15/1 relative to the oxygen containing gas. When the photolithographic substrate reaches the target temperature, a plasma from the process gas is ignited and the substrate is processed by the plasma. Further, the processing of the substrate may be modulated based on time (eg amplitude modulation or pulse modulation). When the processing is completed, the substrate is taken out from the vacuum chamber.

  Another feature of the present invention is to provide a method of processing a photolithographic substrate (eg, a two-layer chromium photomask or an embedded attenuated phase shift mask). The method includes a step of controlling the substrate temperature to a target temperature. In this step, the temperature is controlled by a fluid (for example, an inert gas having a pressure lower than about 1 Torr) during a period in which the substrate is subjected to processing such as etching in a vacuum chamber. The fluid may be temperature controlled and may pass continuously through the vacuum chamber. In addition, at least one surface of the vacuum chamber may be temperature controlled, in which case the surface may be located about 5 cm away from the photolithographic substrate surface. The support that supports the photolithographic substrate in the vacuum chamber may be configured to contact at least three points to maintain minimal contact with the substrate. When the processing is completed, the substrate is taken out from the vacuum chamber.

  Yet another feature of the present invention is to provide a method for etching a photolithography substrate (eg, a two-layer chromium photomask) in a vacuum chamber. The method includes the step of introducing at least one process gas into the vacuum chamber. A first plasma from the process gas is ignited, and the photolithographic substrate is etched using the first plasma under a first set of process conditions. The first set of process conditions may be set so that the antireflection layer of the photolithography substrate is etched. Further, the photoresist layer on the photolithography substrate may be subjected to a stripping process before the process of completely removing Cr remaining on the substrate. The photolithographic substrate is cooled to a target temperature before further processing. The cooling of the photolithographic substrate may be performed in a vacuum chamber in which it is processed, or may be performed in another chamber (the vacuum does not necessarily need to be maintained). When the photolithographic substrate is cooled to a target temperature, a second plasma from the process gas is ignited and the second plasma is used to produce the photo under a second set of process conditions. The lithography substrate is etched. When the processing is completed, the substrate is taken out from the vacuum chamber.

Yet another feature of the present invention is to provide a method for controlling substrate temperature using a large thermal mass during the plasma process. The method includes the step of adjusting the temperature of the substrate on the substrate support in the vacuum chamber. At least one process gas is introduced into the vacuum chamber. Plasma from the process gas is ignited and the substrate for photolithography is processed by the plasma. The substrate may be thermally isolated from the substrate support. Further, the plasma process may be designed to apply a thermal load of less than 0.5 watt / cm ² to the substrate. When the processing is completed, the substrate is taken out from the vacuum chamber.

  Yet another feature of the present invention is to provide a method for processing a photolithographic substrate (eg, a two-layer chromium photomask or a MoSiON phase shift photomask) on a substrate support in a vacuum chamber. The method includes the step of introducing at least one process gas into the vacuum chamber. Plasma from the process gas is ignited and the photolithography substrate is etched using the plasma under a first target temperature and a first set of process conditions. The plasma is then used to etch the photolithographic substrate under a second target temperature and under a second set of process conditions. The second target temperature may be higher or lower than the first target temperature depending on the material to be etched from the photolithography substrate. The cooling or heating of the substrate for photolithography may be performed in a vacuum chamber in which it is processed, or may be performed in another chamber (the vacuum does not necessarily need to be maintained). Further, the first set of process conditions may be set to etch the antireflective layer of the photolithography substrate, and the photoresist layer on the photolithography substrate remains on the substrate. A stripping process may be performed before the process of completely removing Cr. Alternatively, the first set of process conditions may be set to etch the MoSiON layer of the MoSiON phase shift photomask, and the etching stops at the interface of the MoSiON layer and the MoSiON phase shift photomask. Good. When the processing is completed, the substrate is taken out from the vacuum chamber.

  The foregoing has outlined rather broadly some of the more relevant and important aspects of the present invention. Such an overview is intended to facilitate a better understanding of the detailed description of the invention described below, thereby more closely assessing its contribution to the related art. Additional features of the invention will be mentioned in the following description, which forms the subject of the claims of the invention. It should be appreciated by those skilled in the relevant art that the concepts and specific embodiments disclosed herein can be readily applied as a basis for modification or other structural design to achieve the same objectives as the present invention. Furthermore, it is to be understood by those skilled in the relevant art that such equivalent constructions do not depart from the spirit and scope of the invention as defined in the appended claims.

  In all the figures of the attached drawings, like parts are given like numbers.

(Detailed description of the invention)
Embodiments of the present invention will be described with reference to an inductively coupled plasma chamber. An example of a suitable etch chamber is the Mask Etcher IV platform (Oerlikon USA, St. Petersburg, FL). Other reactor configurations can also be used for carrying out the process of the invention. Such reactors include capacitively coupled reactors (eg, reactive ion etchers (RIE), plasma enhanced (PE) reactors, triode reactors, etc.), high density reactors (eg, ICP, TCP, etc.). And magnetically enhanced reactors (eg, ECR, magnetically enhanced reactive ion etcher (MERIE), etc.).

  FIG. 1 is a schematic diagram of an ICP plasma reactor. Multiple types of process gases are introduced into the processing chamber 150 from the gas inlet 120. The process gas mixture is typically controlled by a mass flow controller (not shown). The processing chamber 150 includes a chamber wall 100 and an energy permeable chamber surface 110. The chamber wall 100 is typically made of metal (eg, aluminum, steel, etc.), and the energy permeable chamber surface 110 is typically made of a dielectric material (eg, ceramic). The plasma zone 145 is defined by the chamber wall 100, the substrate support 135 and the energy permeable chamber surface 110. High frequency energy from the high frequency generator 115 is supplied to the inductor 105. The high frequency energy from the generator 115 is temporally modulated (for example, modulation of amplitude, frequency, etc.). The high frequency energy is transmitted to the plasma zone 145 through the energy permeable chamber surface 110. High frequency energy is efficiently transferred from the high frequency generator 115 to the plasma zone 145 by a network (not shown) for matching impedance.

  The substrate support 135 is disposed in the processing chamber and supports the photolithography substrate during the process. The substrate support 135 is connected to the voltage supply device 140. When the voltage supplied to the substrate support 135 is a high-frequency voltage, a network (not shown) for matching impedance is inserted between the bias voltage supply device 140 and the substrate support 135. The high frequency bias may be controlled with respect to voltage or power. The high-frequency supply device 140 may be temporally modulated (for example, modulation of amplitude, frequency, etc.).

  In a typical dry etch process, the substrate is in thermal contact with a temperature controlled substrate support to actively control its temperature. This is typically accomplished by a technique known in the relevant industry as backside cooling with helium, where the substrate is mechanically or electrostatically secured to the substrate support. When mechanically fixed, the fastener is brought into physical contact with the side or top surface of the substrate to maintain its contact with the substrate support. Once the substrate is fixed, a gas (eg, helium) is introduced into the space between the substrate support and the wafer to facilitate heat transfer between the substrate and the substrate support. In order to actively achieve substrate temperature control, the gas pressure of the wafer and substrate support is typically maintained at a pressure higher than 3 Torr. As an alternative to temperature control, the substrate may be electrostatically fixed to the substrate support. Also in this case, a similar back gas is introduced. In the case of electrostatic fixation, since only the back surface of the substrate is brought into contact, it is difficult to fix when the substrate is a dielectric. When the voltage for electrostatic fixation is sufficiently high, it is possible to fix “via the substrate” to the conductor or semiconductor layer disposed on the upper surface of the substrate.

  Because photolithographic substrates are highly defect sensitive, contact with them is traditionally constrained to the 10 mm wide outer edge on the back of it. In the case of dry etching processes, such additional contact restrictions make it impossible to fix the photolithographic substrate. Here, if the mass of a typical substrate support is considered, heat transfer at a low pressure (less than 1 Torr in the case of a current 150 mm photomask substrate) is performed between the substrate and the cathode without fixing the substrate. Note that a working gas can be introduced. Since heat transfer to the substrate by low pressure gas is limited, if the gas pressure to the backside is less than 1 Torr, it is typically insufficient for active temperature control of the substrate. Accordingly, the temperature of the photomask substrate increases during the period in which it is exposed to the plasma.

  FIG. 2 shows that the substrate 130 is optionally disposed on the substrate cover plate 205. The cover plate 205 may be in thermal contact with the substrate support 135 or may be thermally isolated from it. The cover plate 205 is disposed on the substrate support 135. The cover plate 205 is typically provided with a recess, and the recess is designed so that the substrate is accommodated therein and the upper surface of the substrate and the upper surface of the cover plate are substantially in the same plane. The cover plate is in contact with the mask only on the outer edge of the back surface of the reticle 215. The contact width on the back of the reticle is typically within 10 mm of its outer edge. The contact between the reticle and the cover plate may be a continuous ledge (shelf-like horizontal ledge), a point contact, or a combination thereof. Since the cover plate 205 contacts the reticle 130 only at the outer edge of the back surface thereof, there is typically a thin gap 210 between the back surface of the substrate 130 and the substrate support 135.

  The substrate support temperature is controlled by contact with a heat transfer fluid (not shown) during the process, but the amount of heat transfer between the substrate 130 and the cover plate 205 is negligible. Thus, in the absence of helium backside cooling, the photolithographic substrate is heated by the plasma during the dry etching process. The heating rate during the process period is a function of the process factor, and examples of such a factor include high-frequency power and room wall temperature. Photolithographic substrates are typically not actively cooled during the dry etching process. Accordingly, its temperature increases during the period in which the substrate is exposed to the plasma.

In a typical ICP etching process for processing a photolithographic substrate, the thermal load on the substrate is less than about 0.5 W / cm ² . Because the thermal mass of the photolithographic substrate is relatively large, the rate of temperature rise during the dry etch process without aggressive cooling is minimized (typically less than about 2 ° C./min). The total temperature rise for a typical plasma process for etching a photolithographic substrate is less than about 40 ° C.

  In some cases, a barrier against diffusion (not shown) may be disposed on the cover plate to improve etching uniformity.

  Process gas and reaction byproducts are removed through vacuum outlet 125. A throttle valve (not shown) is installed in the outlet to control the chamber pressure during the dry etching process.

  FIG. 3 is a block diagram showing the process flow. The process starts with dry etching of a photolithographic substrate coated with a film. An etch resistant mask is placed on the substrate and patterned by methods known in the relevant industry. The substrate is then cooled to a temperature below about −30 ° C. Once cooled, the substrate is treated with plasma to remove the exposed material with an etch resistant mask.

  Optionally, at the end of the dry etching process, the substrate is heated to about 20 ° C. and then subjected to atmospheric conditions. Heating the substrate prior to placing it under atmospheric conditions prevents condensation that can impair mask performance. The heating step may be performed in a plasma reactor. A reactive gas mixture (for example, an oxygen-containing gas mixture for removing the remaining etching photoresist) or a non-reactive gas (for example, He, Ar, etc.) may be used for the plasma heating step.

  The cooling step before etching may be performed in the plasma etching chamber or in another chamber. During the cooling step, the pressure in the room in which it is performed may exceed atmospheric pressure, may be close to atmospheric pressure, or may be lower. In any case, the cooling atmosphere must be kept clean and dry to prevent the formation of foreign matters or defects due to condensation on the plate to be processed.

  If it is not possible to cool the substrate to maintain a sufficiently low temperature during the entire etching process, the process may be divided into multiple parts (eg, etching is stopped and the substrate is stopped). And then restart the etching process). Such a cycle may be repeated as many times as necessary.

  When a process comprising a plurality of steps is employed (for example, processing of a chrome reticle made of two layers), the substrate may be cooled between etching steps. Recall that the substrate is not actively cooled during the plasma process. Thus, the substrate temperature increases as the plasma process steps progress. If it is desirable to heat the substrate between processes, the substrate may be heated by non-reactive plasma.

  It has also been observed that Cr / antireflective Cr selectivity increases when the temperature is below -90 ° C. When the temperature is −40 ° C., the etching selectivity of Cr / antireflection Cr is approximately 1/1. When the temperature is −140 ° C., the etching selectivity of Cr / antireflection Cr is approximately 3/1. Based on these observations, anti-reflective chromium may be used as an etching mask for the underlying chromium when the substrate temperature is low.

  4a-4d are schematic diagrams of a typical etching process for processing a photomask. In the case where the photomask is made of two layers of chromium, FIG. 4a shows an example of the mask structure before the etching process. The structure has an optically transparent substrate 415. Roughly speaking, the transparent substrate is defined to transmit light having a wavelength of 300 nm or less (for example, 248, 193, or 157 nm), but is not limited thereto. The opaque layer 410 is disposed on the substrate 415. The opaque layer may be composed of a metal (eg, chromium) or other suitable material.

An anti-reflective (AR) layer 405 is disposed on the opaque layer 410. The AR layer 405 is considered to improve the photographic performance of the mask, and may be composed of a metal derivative (eg, metal oxide, nitride, carbide, oxynitride, etc.). Layer 400 is an etch resistant mask used to pattern the underlying opaque and AR layers. The etching resistant mask may be made of a polymer material (eg, photoresist or electron beam resistant material) or a hard disk material (eg, SiO ₂ , SiN, DLC, etc.), which is performed before that. It is patterned in the process step.

  FIG. 4b is a schematic diagram of an etching process for processing a photomask for removing an antireflection (AR) coating layer. If the layer is a chromium-containing film, a chlorine-based etching process is employed. The flow rate of the chlorine-containing gas is typically in the range of about 50 to 400 sccm. The AR layer etch process may optionally use an oxygenated process gas, where the oxygenated gas concentration is from 0 to about 50% of the total process gas flow. The process gas mixture may also contain an inert gas, in which case the inert gas concentration is typically from 0 to about 20% of the total process gas stream.

  In an etching process using ICP, the power for etching the AR layer is typically in the range of about 100-1000W. The high frequency bias power is typically in the range of about 1-30W. The high frequency bias power may be voltage controlled. The process pressure is typically in the range of about 1-20 mtorr.

  FIG. 4 c is a schematic diagram of an etching process (and an excessive etching process) for removing the opaque layer 410. If the layer is a chromium-containing film, an etching process using chlorine-containing and oxygen-containing gases is employed. The flow rate of the chlorine-containing gas is typically in the range of about 50 to 400 sccm. The oxygen-containing gas concentration is about 2-50% of the total process gas flow. The process gas mixture may also contain an inert gas, in which case the inert gas concentration is typically from 0 to about 20% of the total process gas stream. The process factor in the overetching step may be the same as or different from the factor in the etching step that treats the opaque layer. For example, it is not uncommon to increase the oxygen concentration in the overetching process of the opaque layer for the purpose of improving the profile of features.

  FIG. 4d is a schematic diagram of a typical photomask etch showing the process of removing the photoresist layer 400. FIG.

  In an etching process using ICP, the power for etching the opaque layer is typically in the range of about 100-1000W. The high frequency bias power is typically in the range of about 1-30W. The high frequency bias power may be voltage controlled. The process pressure is typically in the range of about 1-20 mtorr.

  Regular type substrates may be clamped and cooled to perform at temperatures below room temperature, but clamping the photographic substrate to clamp the backside during the plasma process is a matter of handling. Not practical due to the above constraints. Photographic substrates have a relatively large thermal mass compared to conventional substrates (for example, a 6 inch square fused silica photomask substrate has a thermal mass of about 221 J / K, whereas silicon of the same size). • That of the wafer is about 17 J / K). With the development of a relatively large thermal mass photographic substrate, if the substrate is cooled prior to the etching process, a low temperature process can be performed without actively cooling it during the etching process. Since the thermal mass of the substrate is large, the temperature rise of the substrate for photolithography is less than 40 ° C. compared to the start of the process due to the use of relatively low high-frequency power and the reduction of processing time. During the period of exposure to plasma, the substrate temperature rises monotonously.

FIGS. 5a and 5c show example results of normal dry etching with low Cr density patterns using Cl ₂ / O ₂ at room temperature (20 ° C.). In both cases, the slope of the feature profile subjected to the etching process is steep, which is disadvantageous in view of the optical performance of the photomask.

The inventors of the present invention have found that the Cr profile subjected to the etching treatment is greatly changed by lowering the substrate temperature. FIGS. 5b and 5d show examples of the results of dry etching with a low Cr density pattern using Cl ₂ / O ₂ at a substrate temperature of −90 ° C. Note that the etching profile is considerably improved according to the results of FIG. 5b. On the other hand, the result of FIG. 5d shows that the positive slope has changed to a negative undercut profile.

  The present invention employed in the etching process of the two-layer chromium photomask has been described above. However, the present invention is not limited to other photographic substrates (for example, half-tone phase shifted mask (Embedded Attenuated Phase Shift Mask, EAPSM). And a dry etching process for a Levenson type phase shift mask (PSM).

  In the manufacture of EAPSM photomasks, it is known in the relevant industry to etch molybdenum silicide (MoSi) and silicon oxynitride molybdenum (MoSixNyOz) using a fluorine-containing plasma. During the fabrication of EAPSM masks, it is desirable to achieve high etch selectivity between the phase shift material and the underlying substrate. To achieve this selectivity, a lower ion energy (lower applied high frequency bias) process is employed. Although selectivity is improved by reducing the high frequency bias, this comes at the expense of reduced etch anisotropy. That is, the low frequency bias process results in an increase in the isotropic of the feature profile. If the photographic substrate is cooled before the etching process, the etching anisotropy is improved even under a lower high-frequency bias power.

(Example)
Experiments were performed using a commercial Etcher 4 system (Oerlikon USA, St. Petersburg, FL), which is a commercially available etcher. In the etching process of a two-layer chromium photograph, it is desirable to achieve a high selectivity for the photoresist in addition to ensuring a high fidelity transfer of the pattern from the photoresist to the Cr. Employing high ICP power (> 200 W) and low oxygen concentration process conditions that would result in Cr / photoresist selectivity exceeding 2/1 when the substrate is at room temperature results in a non-vertical Cr profile, and / Or fidelity of pattern transfer is insufficient. Lowering the substrate temperature can make use of spaces that were previously not economically viable.

注：両マスクは終点（レーザー反射率により決定される終点）までエッチング処理を受け、次いで同じプロセス条件下で５０％の過剰エッチング処理を受けた。 In one experiment, four photomasks were etched using the Oerlikon Mask Etcher 4 system. The first two masks (masks 2983 and 2982) were performed at room temperature by the following two different etching processes.

Note: Both masks were etched to the end point (end point determined by laser reflectivity) and then 50% over-etched under the same process conditions.

In the etching process of the mask 2984 and the mask 2981, both were cooled to about −90 ° C. before the process.
In this process module, the cooled mask was processed under the same process conditions as for a room temperature process mask:

  The etch rate varied depending on both temperature and oxygen concentration. At low oxygen concentrations, the etch rate during low temperature processing increased by about 4%. At a high oxygen concentration, the etching rate during the low temperature treatment decreased by about 23%. The selectivity for photoresist at high oxygen concentration was almost the same at any temperature. At low oxygen concentrations, a significant improvement in selectivity was observed during low temperature processing. Examining the etching rate of the photoresist in detail, the selectivity between the ARC layer and most of the Cr layer also changed depending on both the temperature and the oxygen concentration.

  FIG. 5 shows the Cr profile etched with each mask. From these profiles, it is clear that both oxygen and the temperature of the substrate prior to treatment have a considerable effect on the profile. Low temperature experiments tend to give a more vertical or undercut profile, and room temperature experiments tend to give a more inclined profile. Oxygen serves to give a profile that is more inclined (ie less undercut) in low oxygen concentration experiments than in high oxygen concentration experiments.

This specification describes the appended claims along with the above description. Although the present invention has been described with reference to preferred embodiments with some specificity, the preferred embodiments herein have been described by way of example only, and without departing from the spirit and scope of the present invention, It should be understood that many changes are possible with regard to the details of the combination and arrangement of parts.
The present invention has been described above.

1 is a schematic diagram of a typical ICP plasma system. FIG. It is a schematic diagram of a base support body. It is a block diagram which shows the process flow of this invention. FIG. 4a is a schematic diagram of a typical etching process for processing a photomask showing the mask structure before the etching process. FIG. 4b is a schematic diagram of a typical etching process for processing a photomask for removing the anti-reflective coating layer. FIG. 4c is a schematic diagram of a typical etching process for processing a photomask for removing the opaque layer. FIG. 4d is a schematic diagram of a typical etching process for processing a photomask for removing a photoresist layer. FIG. 5a is a scanning electron micrograph showing the etching result according to the prior art. FIG. 5b is a scanning electron micrograph showing the etching result according to the present invention. FIG. 5c is a scanning electron micrograph showing the etching result according to the prior art. FIG. 5d is a scanning electron micrograph showing the etching result according to the present invention.

Claims (10)

A method of processing a photolithographic substrate comprising the following steps:
Mounting a photolithography substrate in a vacuum chamber;
Before performing the process using the plasma in the vacuum chamber with respect to the photolithographic substrate, as engineering to cool the base body to a temperature lower than -30 ° C.;
Introducing at least one process gas into the vacuum chamber;
Igniting plasma from the process gas after the cooling step;
Processing the photolithography substrate using the plasma, not actively cooling the substrate during the processing; and removing the photolithography substrate from the vacuum chamber.   The method of claim 1, wherein the photolithographic substrate is a two-layer chromium-containing photomask.   The method of claim 1, wherein the photolithographic substrate is a phase shift photomask.   4. The method of claim 3, wherein the phase shift photomask is an embedded attenuated phase shift mask.   The method of claim 1 wherein the treatment step is a plasma etching step.   6. The method of claim 5, wherein the process gas further comprises a chlorine containing gas and an oxygen containing gas.   The method of claim 6, wherein the chlorine-containing gas and the oxygen-containing gas are introduced into the vacuum chamber at a ratio higher than 15/1.   The method of claim 1, further comprising modulating the photolithographic substrate based on time.   9. The method of claim 8, wherein the modulation is amplitude modulation.   9. The method of claim 8, wherein the modulation is pulse modulation.

Images